Researchers make ‘liquid-like’ materials breakthrough

The researchers said the study could lead to the design of new materials that actively transition from fluid-like to solid-like behaviour – via a more advanced understanding of a phenomenon known as ‘jamming’.

Our findings extend shear jamming beyond dry granular materials and demonstrate its relevance to dense particle suspensions too

Lead researcher Ivo Peters

“Add more cars to traffic or more particles to a liquid and the result is a sudden transformation in behaviour from liquid-like flowing to solid-like jammed,” explained Ivo Peters, lecturer in the Aerodynamics and Flight Mechanics Research Group at the University of Southampton, who conducted the work while at the University of Chicago.

“We found a second route to jamming that might appear highly counter-intuitive: solidification without [the] addition of extra particles or changes in volume, but instead triggered by stirring,” Peters added.

He said the research team was able to demonstrate how solidification occurred via fast-moving shear-jamming fronts, which separated the rigidly-jammed state from its slow-moving precursor.

“Our findings provide a new understanding of jamming-related phenomena across a wide range of both microscopic and macroscopic systems,” Peters said.

According to the researchers, their work presents the first systematic experimental study of shear jamming in fully three-dimensional systems, which was conducted by rotating a cylinder, partially submerged in a fluid mixture containing water, glycerol and cornstarch.

The solid behaviour was demonstrated by dropping 5mm spheres onto the continuously sheared material. As more shear was applied to the solution, the spheres’ trajectories changed from slowly sinking (unjammed) to re-bounding and remaining on the surface for as long as the shear-stress was applied (jammed), the researchers said.

“Our findings extend shear jamming beyond dry granular materials and demonstrate its relevance to dense particle suspensions too. Both have their own state diagrams, and we have shown in a single experimental system how a state diagram can be constructed that is compatible with experiments and simulations in both fields,” Peter said.

“Besides unifying the fields, shear jamming in dense suspensions has its own unique feature: the formation of fast propagating shear-jamming fronts, a phenomenon that does not exist in dry systems.”

Dense suspensions are liquid-like materials with particles, and are found in the food manufacturing industry – such as within molten chocolate – and clay deposits on the bottom of oceans or rivers, for instance.

A full account of the research has been published in the journal Nature.